[PDF] Mechanistic Studies And Catalyst Development Of Palladium Catalyzed Aerobic C H Oxidations Of Heteroaromatics eBook

Author : Dian Wang
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Page : 0 pages
File Size : 35,12 MB
Release : 2017
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The selective oxidation of C-H bonds in (hetero)aromatics provides an efficient access to functionalized aromatic molecules of industrial interest. Aerobic oxygen is an ideal terminal oxidants for this transformation because it is readily available and often produces water as the sole byproduct. Homogeneous palladium catalysts are eminently compatible with aerobic turnovers and have seen success in numerous aerobic oxidation processes (e. g., alkene oxidation, alcohol oxidation). In contrast, palladium-catalyzed aerobic oxidative C-H functionalization has been rather underdeveloped. Challenges include slow catalytic turnover, catalyst decomposition and lack of selectivity control (e.g., site selectivity, homo- vs. cross-coupling selectivity). This thesis presents three research projects with different approaches to tackle the unsolved problems in the reaction class of palladium-catalyzed aerobic C-H oxidation of (hetero)aromatics. The reaction mechanism of C-H/C-H coupling of [o]-xylene was characterized, which disclosed a novel, bimetallic pathway. Built on this work, the effect of copper cocatalyst in this reaction was investigated, which revealed a non-traditional role of copper salt in oxidative palladium catalysis and led to the discovery of an improved catalyst system. Last, a synthetic methodology for aerobic indole C-H arylation with ligand-controlled site selectivity was developed, which provided efficient access to pharmaceutically-relevant aryl indoles and led to preliminary mechanistic insights into regiocontrol.

Author : P. Henry
Publisher : Springer Science & Business Media
Page : 449 pages
File Size : 34,92 MB
Release : 2012-12-06
Category : Science
ISBN : 940099446X

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The field of organometallic chemistry has emerged over the last twenty-five years or so to become one of the most important areas of chemistry, and there are no signs of abatement in the intense current interest in the subject, particularly in terms of its proven and potential application in catalytic reactions involving hydrocarbons. The development of the organometallic/ catalysis area has resulted in no small way from many contributions from researchers investigating palladium systems. Even to the well-initiated, there seems a bewildering and diverse variety of organic reactions that are promoted by palladium(II) salts and complexes. Such homogeneous reactions include oxidative and nonoxidative coupling of substrates such as olefins, dienes, acetylenes, and aromatics; and various isomerization, disproportionation, hydrogenation, dehydrogenation, car bonylation and decarbonylation reactions, as well as reactions involving formation of bonds between carbon and halogen, nitrogen, sulfur, and silicon. The books by Peter M. Maitlis - The Organic Chemistry of Palladium, Volumes I, II, Academic Press, 1971 - serve to classify and identify the wide variety of reactions, and access to the vast literature is available through these volumes and more recent reviews, including those of J. Tsuji [Accounts Chem. Res. , 6, 8 (1973); Adv. in Organometal. , 17, 141 (1979)], R. F. Heck [Adv. in Catat. , 26, 323 (1977)], and ones by Henry [Accounts Chem. Res. , 6, 16 (1973); Adv. in Organometal. , 13, 363 (1975)]. F. R. Hartley's book - The Chemistry of Platinum and Palladium, App!. Sci. Pub!.

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Page : 632 pages
File Size : 17,10 MB
Release : 2012
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[alpha,beta]-Unsaturated carbonyl compounds are versatile intermediates in the synthesis of pharmaceuticals and biologically active molecules. The research described herein focuses on the development and mechanistic study of Palladium catalysts for direct aerobic dehydrogenation of ketones and aldehydes to afford the corresponding [alpha,beta]-unsaturated carbonyl compounds. The discovery and application of a novel aerobic dehydrogenation catalyst, Pd(DMSO)2(TFA)2, led to selective dehydrogenation of various cyclohexanone derivatives to afford cyclohexenone products that are of synthetic interest. A complementary Pd(TFA)2/4,5-diazafluorenone catalyst was developed for [alpha,beta]-dehydrogenation of acyclic ketones and aldehydes, with useful applications in preparing unsaturated heterocyclic carbonyl compounds. Characterization of the solution-phase structure of the Pd(DMSO)2(TFA)2 catalyst by NMR spectroscopy suggested that the bis-DMSO ligation to PdII was favorable under the catalytic conditions. Further kinetic studies of Pd(DMSO)2(TFA)2-catalyzed dehydrogenation of cyclohexenone revealed that the DMSO ligands kinetically control the selectivity of dehydrogenation. A fundamental study of the influence of O2 on the acetoxylation of ([pi]-allyl)Pd complexes is also detailed. The fact that O2 is capable of promoting reductive C-O bond formation of ([pi]-allyl)Pd complexes has important implications in understanding the interaction between Pd and O2 and provides a basis for development of Pd-catalyzed aerobic allylic acetoxylation of alkenes.

Author : Maaz S. Ahmed
Publisher :
Page : 0 pages
File Size : 20,7 MB
Release : 2017
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Development of aerobic oxidation methods is of critical importance for the advancement of green chemistry, where the only byproduct produced is water. Recent work by our lab has produced an efficient Pd based heterogenous catalyst capable of preforming the aerobic oxidation of a wide spectrum of alcohols to either carboxylic acid or methyl ester. The well-defined catalyst PdBi0.35Te0.23/C (PBT/C) catalyst has been shown to can perform the aerobic oxidation of alcohols to carboxylic acids in basic conditions. Additionally, we explored this catalyst for a wide range of alcohols and probed the nature of the selectivity of PBT/C for methyl esterification over other side products. Finally, means by which the catalyst operates with respect to oxidation states of the three components, Pd, Bi, and Te, was probed. Carboxylic acids are an important functional group due to their prevalence in various pharmaceutically active agents, agrochemicals, and commodity scale chemicals. The well-defined catalyst PBT/C catalyst was discovered to be effective for the oxidation of a wide spectrum of alcohols to carboxylic acid. The demonstrated substrate scope and functional group tolerance are the widest reported for an aerobic heterogeneous catalyst. Additionally, the catalyst has been implemented in a packed bed reactor with quantitative yield of benzoic acid maintained throughout a two-day run. Biomass derived 5-(hydroxymethyl)furfural (HMF) is also oxidized to 2,5-furandicarboxylic acid (FDCA) in high yield. Exploration of PBT/C for the oxidative methyl esterification was found to exhibit exquisite selectivity for the initial oxidation of primary alcohol instead of methanol, which is the bulk solvent. We explored this selectivity and conclude that it results from various substrate-surface interactions, which are not attainable by methanol. The primary alcohol can outcompete the methanol for binding on the catalyst surface through various interactions between the side chain of the alcohol solvent and the surface of the catalyst: (listed in order of strength) lone pair-surface (heterocyclic primary alcohols)> [pi]-surface (aryl primary alcohols)> van der Waals-surface (alkyl primary alcohols). These interactions were previously underappreciated in condensed phase heterogeneously catalyzed aerobic oxidations. Bi and Te serve as synergistic promoters that enhance both the rate and yield of the reactions relative to reactions employing Pd alone or Pd in combination with Bi or with Te as the sole promoter. We report X-ray absorption spectroscopic studies of the heterogenous catalyst. These methods show that the promoters undergo oxidation in preference to Pd, maintaining the Pd surface in the active metallic state and preventing inhibition by surface Pd-oxide formation. The data also suggest formation of a Pd-Te alloy phase that modifies the electronic properties of the Pd catalyst. Collectively, these results provide valuable insights into the synergistic benefits of multiple promoters in heterogeneous catalytic oxidation reactions.

Author : Hyung Yoon
Publisher : Springer
Page : 212 pages
File Size : 33,57 MB
Release : 2021-09-03
Category : Science
ISBN : 9783030540791

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This book presents Pd- and Ni-catalyzed transformations generating functionalized heterocycles. Transition metal catalysis is at the forefront of synthetic organic chemistry since it offers new and powerful methods to forge carbon–carbon bonds in high atom- and step-economy. In Chapter 1, the author describes a Pd- and Ni-catalyzed cycloisomerization of aryl iodides to alkyl iodides, known as carboiodination. In the context of the Pd-catalyzed variant, the chapter explores the production of enantioenriched carboxamides through diastereoselective Pd-catalyzed carboiodination. It then discusses Ni-catalyzed reactions to generate oxindoles and an enantioselective variant employing a dual ligand system. Chapter 2 introduces readers to a Pd-catalyzed diastereoselective anion-capture cascade. It also examines diastereoselective Pd-catalyzed aryl cyanation to synthesize alkyl nitriles, a method that generates high yields of borylated chromans as a single diastereomer, and highlights its synthetic utility. Lastly, Chapter 3 presents a Pd-catalyzed domino process harnessing carbopalladation, C–H activation and π-system insertion (benzynes and alkynes) to generate spirocycles. It also describes the mechanistic studies performed on these reactions.

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Page : 232 pages
File Size : 32,63 MB
Release : 2014
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Palladium catalyzed oxidative transformations that employ readily available molecular oxygen as the stoichiometric oxidant enable economic synthetic routes to complex organic targets. This thesis focuses on the development of aerobic oxidative transformations that generate carbon-nitrogen bonds. Chapters 2 and 3 describe research projects that have expanded the scope and mechanistic understanding of reactions that involve amidopalladation of alkenes (aza-Wacker reactions). Chapters 4, 5 and 6 describe research projects that have targeted the discovery of aryl C-H amination reactions. Palladium catalyzed aerobic C-H amination reactions have limited precedent. Several approaches to address this challenge were tested, and promising results are discussed.